There is a statistics smell that he initially shows also 1y and 3y performance for the endowments, but then doesn't show these for his alternative. Probably he cherry-picked the data that supported his point and hid the rest.
From the article "1 and 3 years returns are mostly noise". He focuses on a longer term since it's a much better comparison. On a growing market it's much easier to overperform the index but then get wiped when a crash happens.
For the endowments, the 1y and 3y returns didn't look like noise. Hiding the noisy data is hiding the fact that the ETF strategy is more risky than the endowments.
What do you mean ? The shorter term you look the more noise there is. I'm not sure that it's exactly the same 1y period, you are just averaging out a lot of funds. I would say the fact that ETFs overperformed on a long term means they are less risky not more.